During the drilling of a wellbore, various fluids are typically used in the well for a variety of functions. The fluids may be circulated through a drill pipe and drill bit into the wellbore, and then may subsequently flow upward through the wellbore to the surface. During this circulation, the drilling fluid may act to remove drill cuttings from the bottom of the hole to the surface, to suspend cuttings and weighting material when circulation is interrupted, to control subsurface pressures, to maintain the integrity of the wellbore until the well section is cased and cemented, to isolate the fluids from the formation by providing sufficient hydrostatic pressure to prevent the ingress of formation fluids into the wellbore, to cool and lubricate the drill string and bit, and/or to maximize penetration rate.
In most rotary drilling procedures the drilling fluid takes the form of a “mud,” i.e., a liquid having solids suspended therein. The solids function to impart desired rheological properties to the drilling fluid and also to increase the density thereof in order to provide a suitable hydrostatic pressure at the bottom of the well. The drilling mud may be either a water-based or an oil-based mud.
As an example of a completion fluid, a reservoir drill-in fluid (RDF) is utilized for drilling through a reservoir section of a wellbore. RDF's are typically used for successful reservoir zone drilling, minimizing damage to and maximizing production of exposed zones, and facilitation of the well completion clean-up process.
In particular, direct emulsion systems may not have been used extensively in oil field drilling fluids, such as completion fluids and/or RDF's, due to their relative emulsion instability, sensitivity to common contaminants, and/or susceptibility to undesired reversibility.
Thus, there exists a continuing need for improvements in the completion fluids and/or reservoir drill-in fluids utilizing thermodynamically stable direct emulsion systems.